Single-phase brushless motor drive circuit

ABSTRACT

A driving circuit for a single-phase-brushless motor includes a driving-signal-generating circuit to generate a driving signal for supplying, to a driving coil of the single-phase-brushless motor, first- and second-driving currents alternately with a de-energized period therebetween, an output circuit, and a zero-cross-detecting circuit. While measuring a driving cycle from a start of an energized period, during which the output circuit supplies the first- or the second-driving current to the driving coil, to a time when the zero-cross-detecting circuit detects a zero cross of an induced voltage, generated across the driving coil, during the de-energized period, the driving-signal-generating circuit determines a length of a subsequent energized period based on the measured driving cycle, when the zero-cross-detecting circuit detects the zero-cross, and the driving-signal-generating circuit determines a length of an immediately previous energized period as a length of a subsequent energized period, when the zero-cross-detecting circuit does not detect the zero-cross.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Japanese PatentApplication No. 2011-132553, filed Jun. 14, 2011, of which full contentsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving circuit for a single-phasebrushless motor.

2. Description of the Related Art

A brushless motor among DC motors has advantages such as its long lifesince it does not use any brush or commutator. By employing asingle-phase brushless motor disclosed in Japanese Laid-Open PatentPublication No. 2008-312440, for example, only one position detectingdevice such as a Hall element is sufficient, a single phase is alsosufficient in the driving circuit, and thus cost and size, etc., can bereduced.

Whereas, in a common single-phase brushless motor, a stop positionexists which is referred to as “dead (locked) point” at which a rotor(rotator) thereof does not rotate even when a driving current starts tobe supplied to a driving coil thereof. Thus, the single-phase brushlessmotor in Japanese Laid-Open Patent Publication No. 2008-312440 takescountermeasures to prevent the dead point by stopping at a positionwhere the center of permanent magnets thereof and the center of thedriving coil are deviated from each other. Further, a driving controlcircuit is also disclosed therein that applies a voltage generating acurrent in the direction opposite to that of an induced voltage (counterelectromotive voltage) generated across the driving coil, therebyrealizing improvement in efficiency, reduction in vibration and noise,etc.

As such, taking the countermeasures against the dead point and using thetechniques to reduce vibration and noise as above enable thesingle-phase brushless motor to be used in various uses such as a fanmotor.

Since the single-phase brushless motor is able to be configured to besmall in size at a low cost, a suitable use may be a vibration motorused for a vibration function of a cellular telephone to let a user knowarrival of a call, for example. Especially, when it is used as thevibration motor, a rectangular wave, more likely to generate vibrations,may be used as a driving signal, and thus the motor driving circuit canbe reduced in a circuit scale, and a motor driving IC can be reduced incost and size.

Further, among motor driving ICs, a motor driving IC is also known thatincorporates therein a Hall element to detect a rotation position of arotor. However, since such a Hall-element-incorporating IC needs to bemounted in the interior of the motor, the effect of the miniaturizationthereof is reduced. Further, since an error arises in the precision fordetecting the rotation position of the rotor due to characteristics ofthe Hall element itself during the manufacture of the IC, a test toapply a magnetic field is required before shipment of the motor. Thus,the effect achieved by the cost reduction is reduced.

SUMMARY OF THE INVENTION

A driving circuit for a single-phase brushless motor according to anaspect of the present invention, includes: a driving signal generatingcircuit configured to generate a driving signal for supplying, to adriving coil of the single-phase brushless motor, a first drivingcurrent and a second driving current opposite in direction to the firstdriving current, in an alternate manner with a de-energized periodtherebetween during which neither of the first driving current or thesecond driving current is supplied to the driving coil; an outputcircuit configured to supply the first or the second driving current tothe driving coil in response to the driving signal; and a zero-crossdetecting circuit configured to detect a zero cross of an inducedvoltage, generated across the driving coil, during the de-energizedperiod, wherein while measuring a driving cycle from a start of anenergized period, during which the output circuit supplies the first orthe second driving current to the driving coil, to a time when thezero-cross detecting circuit detects the zero cross, the driving signalgenerating circuit determines a length of a subsequent energized periodbased on the measured driving cycle, when the zero-cross detectingcircuit detects the zero cross, and the driving signal generatingcircuit determines a length of an immediately previous energized periodas a length of a subsequent energized period, when the zero-crossdetecting circuit does not detect the zero cross.

Other features of the present invention will become apparent fromdescriptions of this specification and of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For more thorough understanding of the present invention and advantagesthereof, the following description should be read in conjunction withthe accompanying drawings, in which:

FIG. 1 is a circuit block diagram illustrating a configuration of anentire driving circuit for a single-phase brushless motor according to afirst embodiment of the present invention;

FIG. 2 is a circuit block diagram illustrating an example of specificconfigurations of an output circuit 20 and an induced voltage detectingcircuit 30;

FIG. 3 is a circuit block diagram illustrating a configuration of anedge detecting circuit according to a first embodiment of the presentinvention;

FIG. 4 is a diagram for explaining an operation of a motor drivingcircuit 1 a in a starting-up mode according to a first embodiment of thepresent invention;

FIG. 5 is a diagram illustrating an example of a start-up count(energized time period) set in advance for each loop count value (thenumber of energizations) in a starting-up mode;

FIG. 6 is a diagram for explaining an operation of a motor drivingcircuit 1 a in a normal mode according to a first embodiment of thepresent invention;

FIG. 7 is a diagram for explaining an operation of a motor drivingcircuit 1 a executed when no zero cross of an induced voltage isdetected during a de-energized period according to a first embodiment ofthe present invention;

FIG. 8 is a circuit block diagram illustrating a configuration of anentire driving circuit of a single-phase brushless motor according to asecond embodiment of the present invention;

FIG. 9 is a diagram for explaining an operation of a motor drivingcircuit 1 b executed when no zero cross of an induced voltage isdetected during a de-energized period according to a second embodimentof the present invention;

FIG. 10 is a diagram for explaining an operation of a motor drivingcircuit 1 a (1 b) executed when a zero cross occurs due to a drivingcurrent immediately after a zero cross of an induced voltage is detectedaccording to first and second embodiments of the present invention; and

FIG. 11 is a diagram for explaining an operation of a motor drivingcircuit 1 a (1 b) executed when a zero cross occurs in an inducedvoltage during a non-detection period according to first and secondembodiments of the present invention.

FIG. 12 is a circuit block diagram illustrating a configuration of anedge detecting circuit according to a third embodiment of the presentinvention;

FIG. 13 is a circuit block diagram illustrating a configuration of anedge detecting circuit according to a third embodiment of the presentinvention;

FIG. 14 is a diagram for explaining an operation of a motor drivingcircuit 1 c executed when a zero cross occurs due to a driving currentimmediately after a zero cross of an induced voltage is detectedaccording to a third embodiment of the present invention; and

FIG. 15 is a diagram for explaining an operation of a motor drivingcircuit 1 c executed when a zero cross occurs in an induced voltageduring a non-detection period according to a third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

At least the following details will become apparent from descriptions ofthis specification and of the accompanying drawings.

First Embodiment Configuration of Entire Driving Circuit forSingle-Phase Brushless Motor

A configuration of an entire driving circuit for a single-phasebrushless motor according to a first embodiment of the present inventionwill hereinafter be described with reference to FIG. 1.

A motor driving circuit 1 a depicted in FIG. 1 is a circuit to drive asingle-phase brushless motor including a driving coil 9, and isconfigured as an integrated circuit including at least output terminals91 and 92 connected to the driving coil 9. The motor driving circuit 1 aincludes a main counter 11 a, a driving cycle storing register 12, anenergized time period setting register 13, a loop counter 14, aselecting circuit 15, a timing control circuit 16, a NOR circuit (NOT-ORcircuit) 17, an output circuit 20, an induced voltage detecting circuit30, a comparator (comparator) 40, and an edge detecting circuit 50.

In an embodiment of the present invention, the main counter 11 a, thedriving cycle storing register 12, the energized time period settingregister 13, the loop counter 14, the selecting circuit 15, and thetiming control circuit 16 are equivalent to a driving signal generatingcircuit. The induced voltage detecting circuit 30, the comparator 40,and the edge detecting circuit 50 are equivalent to a zero-crossdetecting circuit.

A clock signal CLK (predetermined clock) is inputted to a CK input(clock input) of the main counter 11 a (first counter circuit), and anedge detection signal EG outputted from the edge detecting circuit 50 isinputted to a CL input (clear input) thereof. A main count value CNT isoutputted from the main counter 11 a.

The main count value CNT and the edge detection signal EG are inputtedto the driving cycle storing register 12, and a normal-operation countvalue Ton is outputted from the driving cycle storing register 12. Astart-up count values T1 to T10 set in advance for each loop count valueLP outputted from the loop counter 14 are outputted from the energizedtime period setting register 13.

The edge detection signal EG is inputted to a CK input of the loopcounter 14 (second counter circuit), and the loop count value LP isoutputted from the loop counter 14. The selecting circuit 15 isconfigured as an eleven-input, one-output multiplexer, and the loopcount value LP is inputted to a select control input thereof. Further,the start-up count values T1 to T10 are respectively inputted tocorresponding data inputs in the case where the loop count values LP are1 to 10, and the normal-operation count value Ton is inputted to acorresponding data input in the case where the loop count value LP isequal to or greater than 11.

The timing control circuit 16 is inputted with the least significant bit(hereinafter, referred to as “odd-even bit LP [0]”) that indicateswhether the loop count value LP is an odd number or an even number,together with the main count value CNT and an output value of theselecting circuit 15. Driving signals S1 and S2 are outputted from thetiming control circuit 16. Further, the driving signals S1 and S2 areinputted to the NOR circuit 17, and a high impedance signal HZ isoutputted from the NOR circuit 17.

The driving signals S1 and S2 are inputted to the output circuit 20, andoutput nodes of the output circuit 20 are connected to the driving coil9 through the output terminals 91 and 92. Respective voltages V1 and V2of the output terminals 91 and 92 are inputted to the induced voltagedetecting circuit 30. An output voltage Vout of the induced voltagedetecting circuit 30 is applied to a non-inverting input of thecomparator 40, and a reference voltage Vref is applied to an invertinginput thereof. A comparison result signal CP is outputted from thecomparator 40. The comparison result signal CP and the high impedancesignal HZ are inputted to the edge detecting circuit 50, and the edgedetection signal EG is outputted from the edge detecting circuit 50.

===Configurations of Output Circuit and Induced Voltage DetectingCircuit===

More specific configurations of the output circuit 20 and the inducedvoltage detecting circuit 30 will be described with reference to FIG. 2.

The output circuit 20 depicted in FIG. 2 is configured as an H-bridgecircuit including output transistors M1 to M4. Hereinafter, adescription will be given, as an example, of a case where the outputtransistors M1 and M2 are PMOS (P-channel Metal-Oxide Semiconductor)transistors and the output transistors M3 and M4 are NMOS (N-channelMOS) transistors.

The output transistor M1 is connected in series to the output transistorM3, and the output transistor M2 is connected in series to the outputtransistor M4. The sources of the output transistors M1 and M2 are bothconnected to a power source VCC, and the sources of the outputtransistors M3 and M4 are both connected to the ground. Further, thedriving signal S1 is inputted to both of the gates of the outputtransistors M1 and M4, and the driving signal S2 is inputted to both ofthe gates of the output transistors M2 and M3. A connection pointbetween the output transistors M1 and M3 is connected to the outputterminal 91, and a connection point between the output transistors M2and M4 is connected to the output terminal 92.

The induced voltage detecting circuit 30 depicted in FIG. 2 isconfigured as a differential amplifier circuit including resistors R1 toR4 and an Op Amp (operational amplifier) OP. One end of the resistor R1is connected to the output terminal 92 and the other end thereof isconnected to an inverting input of the operational amplifier OP. One endof the resistor R2 is connected to the output terminal 91 and the otherend thereof is connected to a non-inverting input of the operationalamplifier OP. One end of the resistor R3 is connected to the invertinginput of the operational amplifier OP and the other end thereof isconnected to an output of the operational amplifier OP. One end of theresistor R4 is connected to the non-inverting input of the operationalamplifier OP and the other end thereof is applied with the referencevoltage Vref.

===Configuration of Edge Detecting Circuit===

A more specific configuration of the edge detecting circuit 50 will bedescribed with reference to FIG. 3.

The edge detecting circuit 50 depicted in FIG. 3 includes delay circuits51 and 53, an XOR circuit (exclusive-OR circuit) 52, and an AND circuit(logical multiplication circuit) 54.

The comparison result signal CP is inputted to the delay circuits 51.The comparison result signal CP and an output signal of the delaycircuit 51 are inputted to the XOR circuit 52. A both-edge signal EGrfis outputted from the XOR circuit 52. The high impedance signal HZ isinputted to the delay circuit 53, and a mask signal MS is outputted fromthe delay circuit 53. The both-edge signal EGrf and the mask signal MSare inputted to the AND circuit 54, and the edge detection signal EG isoutputted from the AND circuit 54.

===Operation of Driving Circuit for Single-Phase Brushless Motor===

An operation of the driving circuit for the single-phase brushless motoraccording to an embodiment of the present invention will hereinafter bedescribed.

The main counter 11 a counts using the clock signal CLK, and outputs themain count value CNT that is incremented by one. The main counter 11 ais reset and the main count value CNT is cleared every time the pulsededge detection signal EG is inputted thereto. In practice, because thebit number of the main counter 11 a is limited, when the main counter 11a counts to a predetermined count value (e.g., full count value), forexample, the main counter 11 a stops counting until it is reset.

The driving cycle storing register 12 stores therein the main countvalue CNT which is immediately before being cleared, as a driving cycle,every time the edge detection signal EG is inputted thereto. The drivingcycle includes an “energized period” during which a driving current issupplied to the driving coil 9 and a subsequent “de-energized period”during which no driving current is supplied to the driving coil 9, aswill be described later. The driving cycle storing register 12 outputs avalue acquired by multiplying the main count value CNT (driving cycle)stored therein by a predetermined coefficient “a” (0<a<1), as thenormal-operation count value Ton that indicates a length of theenergized period in the subsequent driving cycle.

The loop counter 14 counts every time the edge detection signal EG isinputted thereto, and outputs the loop count value LP that isincremented by one. Therefore, the loop counter 14 counts the number ofthe driving cycles from the starting up of the motor driving circuit 1a, i.e., the number of energized periods, and the loop count value LPindicates the number of energizations of the driving coil 9 from thestarting up of the motor driving circuit 1 a. The energized time periodsetting register 13 has the start-up count values T1 to T10 storedtherein that each indicate an energized time period set in advance foreach loop count value LP from 1 to 10.

The selecting circuit 15 outputs the start-up count values T1 to T10respectively when the loop count values LP are one to ten, and outputsthe normal-operation count value Ton when the loop count value LP isequal to or greater than 11. In practice, because the bit number of theloop counter 14 is limited, when the loop counter 14 counts to a value(e.g., 11) for the selecting circuit 15 to output the normal-operationcount value Ton, for example, the loop counter 14 changes only the leastsignificant bit (odd-even bit LP[0]) of the loop count value LP.

The timing control circuit 16 outputs the driving signals S1 and S2based on the main count value CNT, and the output circuit 20 suppliesthe driving current to the driving coil 9 in response to the drivingsignals S1 and S2. Hereinafter, a driving current (first drivingcurrent) flowing through the driving coil 9 in the direction from theoutput terminal 91 to the output terminal 92 is referred to as “positivecurrent”, and a driving current (second driving current) flowingtherethrough in the direction opposite to that of the positive currentis referred to as “negative current”.

More specifically, during a time period from the time when the maincount value CNT is cleared by the edge detection signal EG to the timewhen it reaches an output value of the selecting circuit 15, the timingcontrol circuit 16 sets one of the driving signals S1 and S2 high (at ahigh level). The output circuit 20 supplies, to the driving coil 9, thepositive current (when the driving signal S1 is high) or the negativecurrent (when the driving signal S2 is high).

Whereas, during a time period from the time when the main count valueCNT reaches the output value of the selecting circuit 15 to the timewhen it is cleared by the edge detection signal EG, the timing controlcircuit 16 sets both of the driving signals S1 and S2 low (at a lowlevel). The output circuit 20 supplies neither of the positive currentand the negative current to the driving coil 9.

The timing control circuit 16 switches the driving signal, which is tobe high during the energized period, in response to the odd-even bit LP[0]. Thus, the timing control circuit 16 switches between the positivecurrent and the negative current to be supplied by the output circuit 20to the driving coil 9, every time the odd-even bit LP [0] is changed bythe edge detection signal EG.

As such, the timing control circuit 16 controls the energized period andthe de-energized period, and the output circuit 20 supplies the positivecurrent and the negative current to the driving coil 9 in an alternatemanner with the de-energized period therebetween in accordance with thecontrol of the timing control circuit 16. The NOR circuit 17 outputs thehigh impedance signal HZ which is high during the de-energized periodduring which the driving signals S1 and S2 both are low and the outputof the output circuit 20 is in a high impedance state.

The induced voltage detecting circuit 30 amplifies a differentialvoltage V1−V2 of the voltages V1 and V2 and outputs the amplifiedvoltage, thereby detecting an induced voltage generated across thedriving coil 9 during the de-energized period. In this case, bysatisfying the relationship of R1=R2 and R3=R4, the output voltage Voutof the induced voltage detecting circuit 30 results inVout=Vref+(R3/R1)·(V1−V2).The comparator 40 compares the output voltage Vout with the referencevoltage Vref, and outputs the comparison result signal CP, which goeshigh when the comparison result is Vout>Vref, that is, when thedifferential voltage V1−V2 is positive, and which goes low when it isnegative.

The XOR circuit 52 of the edge detecting circuit 50 detects a risingedge and a falling edge of the comparison result signal CP by acquiringthe exclusive-OR of the comparison result signal CP and a delay signalthereof (output signal of the delay circuit 51), and outputs the pulsedboth-edge signal EGrf. Thus, the both-edge signal EGrf indicates thetiming of a zero cross at which the sign of the differential voltageV1−V2 switches from positive to negative or form negative to positive.

The delay circuit 53 outputs the mask signal MS acquired by delaying thehigh impedance signal HZ, so as to mask the zero cross due to thedriving current passed through the driving coil during the energizedperiod (positive current or negative current) and/or by a regenerativecurrent passed when the period is shifted from the energized period tothe de-energized period. The AND circuit 54 masks the both-edge signalEGrf using the mask signal MS and outputs the edge detection signal EG.

As such, the zero-cross detecting circuit (the induced voltage detectingcircuit 30, the comparator 40, and the edge detecting circuit 50)detects the zero cross of the induced voltage generated across thedriving coil 9 during the de-energized period, and outputs the pulsededge detection signal EG.

===Specific Example of Operation of Driving Circuit for Single-PhaseBrushless Motor===

A specific example of an operation of the driving circuit for thesinge-phase brushless motor according to an embodiment of the presentinvention will be described with reference to FIGS. 4 to 6 asappropriate. Hereinafter, an operation mode in which the loop countvalue LP is from 1 to 10 will be referred to as “starting-up mode”, andan operation mode, which follows thereafter, will be referred to as“normal mode”. A positive current flows through the driving coil 9 whenthe loop count value LP is an odd number (LP [0]=1), and a negativecurrent flows through the driving coil 9 when the loop count value LP isan even number (LP[0]=0).

An operation of the motor driving circuit 1 a in the starting-up mode(LP≦10) will be described with reference to FIG. 4. The starting-up modeindicates an operation mode from the start-up of the motor drivingcircuit 1 a to the tenth driving cycle. FIG. 4 depicts the first to thefourth driving cycles.

When the motor driving circuit 1 a is started up, the main counter 11 astarts counting using the clock signal CLK, and the first driving cycle(LP=1) is started. The timing control circuit 16 sets the driving signalS1 high, and sets the driving signal S2 low, thereby starting the supplyof the positive current from the output circuit 20 to the driving coil9. During the energized period of the positive current, the differentialvoltage V1−V2 is positive, and the comparison result signal CP is high.

During the energized period of the positive current, when the main countvalue CNT reaches a start-up count value T1 (CNT=T1), the timing controlcircuit 16 sets both of the driving signals S1 and S2 low, therebystopping the supply of both of the positive current and the negativecurrent from the output circuit 20 to the driving coil 9. When theenergized period shifts to the de-energized period, a zero cross occursdue to the regenerative current, however, the zero cross is masked bythe mask signal MS acquired by delaying the high impedance signal HZ bya delay time period D1 of the delay circuit 53.

During the de-energized period, when the zero-cross detecting circuitdetects the zero cross of the induced voltage generated across thedriving coil 9 and outputs the edge detection signal EG having a pulsewidth of a delay time period D2 of the delay circuit 51, the maincounter 11 a is reset and the main count value CNT is cleared (CNT=0).Further, the loop count value LP is incremented and the second drivingcycle (LP=2) is started. The timing control circuit 16 sets the drivingsignal S1 low and sets the driving signal S2 high, thereby starting thesupply of the negative current from the output circuit 20 to the drivingcoil 9. During the energized period of the negative current, thedifferential voltage V1−V2 is negative and the comparison result signalCP is low.

During the energized period of the negative current, when the main countvalue CNT reaches a start-up count value T2 (CNT=T2), the timing controlcircuit 16 sets both of the driving signals S1 and S2 low, therebystopping the supply of both of the positive current and the negativecurrent from the output circuit 20 to the driving coil 9.

During the de-energized period, when the zero-cross detecting circuitdetects the zero cross of the induced voltage and outputs the edgedetection signal EG, the main counter 11 a is reset and the main countvalue CNT is cleared (CNT=0). Further, the loop count value LP isincremented and the third driving cycle (LP=3) is started. The timingcontrol circuit 16 sets the driving signal S1 high and sets the drivingsignal S2 low, thereby starting the supply of the positive current fromthe output circuit 20 to the driving coil 9 again.

As such, in the starting-up mode, the motor driving circuit 1 a suppliesthe positive current or the negative current from the output circuit 20to the driving coil 9 only during the energized time periods indicatedby the start-up count values T1 to T10 respectively set in advance forloop count values LP, and the energized period shifts to thede-energized period. When the zero cross of the induced voltagegenerated across the driving coil 9 is detected during the de-energizedperiod, the positive current and the negative current are switched,thereby shifting to the energized period. Then, these operations arerepeated until the tenth driving cycle (LP=10).

Here, by setting (the energized time periods indicated by) the start-upcount values T1 to T10 so as to decrease with increase in (the number ofenergizations indicated by) the loop count value LP, the motor drivingcircuit 1 a are able to smoothly start up the single-phase brushlessmotor from a halting state to a high-speed rotation state. As depictedas an example in FIG. 5, the start-up count values T1 to T10 are set inadvance to be substantially inversely proportional to the loop countvalue LP. Setting the start-up count values T1 to T10 as such enablesthe motor driving circuit 1 a to further quickly start up thesingle-phase brushless motor.

Next, an operation of the motor driving circuit 1 a in the normal mode(LP≧11) will be described with reference to FIG. 6. The normal modeindicates an operation mode in the eleventh driving cycle andthereafter, and FIG. 6 depicts (n−1)th to (n+2)th driving cycles (“n” isan even number equal to or greater than 12).

In the de-energized period in the (n−1)th driving cycle (LP=n−1), whenthe zero-cross detecting circuit detects the zero cross of the inducedvoltage and outputs the edge detection signal EG, the main counter 11 ais reset and the main count value CNT is cleared (CNT=0). Further, thedriving cycle storing register 12 stores therein the main count valueCNT which is immediately before being cleared, as well as outputs thenormal operation count value Ton acquired by multiplying the stored maincount value CNT by the coefficient “a” (Ton=CNT×a). Here, the normaloperation count value Ton indicates the length of the energized periodin the n-th driving cycle (LP=n), and preferably, is set at about 70% ofthe whole (n−1)th driving cycle (a=0.7).

Further, the loop count value LP is incremented and the n-th drivingcycle is started. Then, the timing control circuit 16 sets the drivingsignal S1 low and sets the driving signal S2 high, thereby starting thesupply of the negative current from the output circuit 20 to the drivingcoil 9.

In the energized period in the n-th driving cycle, when the main countvalue CNT reaches the normal operation count value Ton (CNT=Ton), thetiming control circuit 16 sets both of the driving signals S1 and S2low, thereby stopping the supply of both of the positive current and thenegative current from the output circuit 20 to the driving coil 9.

In the de-energized period, when the zero-cross detecting circuitdetects the zero cross of the induced voltage and outputs the edgedetection signal EG, the main counter 11 a is reset and the main countvalue CNT is cleared (CNT=0). Further, the driving cycle storingregister 12 stores therein the main count value CNT which is immediatelybefore being cleared, as well as outputs the normal operation countvalue Ton (Ton=CNT×a). Further, the loop count value LP is incrementedand the (n+1) th driving cycle (LP=n+1) is started. The timing controlcircuit 16 sets the driving signal S1 high and sets the driving signalS2 low, thereby starting the supply of the positive current from theoutput circuit 20 to the driving coil 9.

As such, in the normal mode, the motor driving circuit 1 a supplies thepositive current or the negative current from the output circuit 20 tothe driving coil 9 only during the energized time period indicated bythe normal operation count value Ton which is acquired by multiplyingthe main count value CNT stored in the driving cycle storing register 12by the predetermined coefficient “a” (0<a<1), and the period shifts tothe de-energized period. In the normal mode started after thesingle-phase brushless motor is started up in the starting-up mode,since variations in the driving cycle are small, the length of thesubsequent energized period is determined, at each time, to correspondto a predetermined proportion to the whole driving cycle immediatelybefore the current cycle. Similarly to the starting-up mode, when thezero cross of the induced voltage generated across the driving coil 9 isdetected during the de-energized period, between the positive currentand the negative current are switched, thereby shifting to the energizedperiod. These operations are repeated in each driving cycle.

Second Embodiment Configurations of Entire Driving Circuit and EntireEdge Detecting Circuit for Single-Phase Brushless Motor

As described above, in the motor driving circuit 1 a according to afirst embodiment of the present invention, every time the edge detectionsignal EG is outputted from the edge detecting circuit 50, the maincount value CNT is cleared, the loop count value LP is incremented, andthe odd-even bit LP [0] is changed. The timing control circuit 16switches between the positive current and the negative current, to causethe driving current to start to be supplied from the output circuit 20to the driving coil 9.

Further, during the energized period, when the main count value CNTreaches any one of the start-up count values T1 to T10 (in thestarting-up mode) or the normal-operation count value Ton (in the normalmode), the timing control circuit 16 causes the driving current to stopbeing supplied from the output circuit 20 to the driving coil 9. Duringthe de-energized period, the zero-cross detecting circuit executesdetection of the zero cross of the induced voltage generated in thedriving coil 9.

However, there may be the case where no zero cross occurs in the inducedvoltage, such as the case where the rotor does not rotate even when thedriving current is supplied to the driving coil 9 during the energizedperiod or the case where the period is shifted to the de-energizedperiod and the driving current is not supplied to the driving coil 9thereby stopping the rotor. Especially, in the starting-up mode (LP≦10),the energized time period is set in advance, and further, in the firstdriving cycle immediately after the starting up (LP=1), the rotor islikely not to rotate or easily stops because the rotor needs to berotated from its halting state.

When no zero cross occurs in the induced voltage and the zero-crossdetecting circuit is unable to detect any zero cross occurring in theinduced voltage during the de-energized period, the edge detectionsignal EG is not outputted and the de-energized period continues asdepicted in FIG. 7, for example. Thus, in the motor driving circuit 1 a,since it is impossible to shift to the energized period again, the rotorcontinues to be in the halting state.

Hereinafter, a description will be given, with reference to FIG. 8, of aconfiguration of the entire driving circuit for the single-phasebrushless motor according to a second embodiment of the presentinvention, which is capable of securely rotating the rotor even when nozero cross occurring in the induced voltage is detected during thede-energized period.

The motor driving circuit 1 b depicted in FIG. 8 includes a main counter11 b in place of the main counter 11 a and further includes an ORcircuit (logical sum circuit) 18, with respect to the motor drivingcircuit 1 a according to a first embodiment of the present invention.

The clock signal CLK is inputted to a CK input of the main counter 11 b(first counter circuit) similarly to the main counter 11 a. A restartsignal RES is outputted from the main counter 11 b in addition to themain count value ONT. The restart signal RES and the edge detectionsignal EG are inputted to the OR circuit 18 and an output signal of theOR circuit 18 is inputted to a CL input of the main counter 11 b.

===Operation of Driving Circuit of Single-Phase Brushless Motor===

Hereinafter, an operation of the driving circuit for the single-phasebrushless motor according to an embodiment of the present invention willbe described with reference to FIG. 9 as appropriate. The operation ofthe motor driving circuit 1 b according to an embodiment of the presentinvention is similar to the operation of the motor driving circuit 1 aaccording to a first embodiment of the present invention except foroperations of the main counter 11 b and the OR circuit 18.

Similarly to the main counter 11 a, the main counter 11 b counts usingthe clock signal CLK and outputs the main count value CNT that isincremented by one. When counting to a predetermined count value (firstpredetermined value), the main counter 11 b outputs the restart signalRES. In an embodiment of the present invention, as an example, whencounting to a full count value Tmax, the main counter 11 b outputs therestart signal RES. Therefore, the main counter 11 b is reset every timethe zero cross detecting circuit detects the zero cross of the inducedvoltage and outputs the pulsed edge detection signal EG, or when themain count value CNT reaches the full count value Tmax.

As such, in the motor driving circuit 1 b according to an embodiment ofthe present invention, when the main count value CNT reaches the fullcount value Tmax, the main counter 11 b is also reset and the main countvalue CNT is also cleared. In this case, the loop count value LP is notincremented, and as depicted in FIG. 9, for example, the timing controlcircuit 16 causes the driving current to start to be supplied from theoutput circuit 20 to the driving coil 9 without switching between thepositive current and the negative current.

Since the loop count value LP is not incremented, in the starting-upmode, the output value of the selecting circuit 15 becomes equal to thatof the immediately previous driving cycle and the length of theimmediately previous energized period is determined to be the length ofthe subsequent energized period. Further, the main count value CNTimmediately before being cleared (i.e., the full count value Tmax) isnot stored in the driving cycle storing register 12, and thus, in thenormal mode as well, the output value of the selecting circuit 15 alsobecomes equal to that of the immediately previous driving cycle and thelength of the immediately previous energized period is determined to thelength of the subsequent energized period.

Therefore, in the motor driving circuit 1 b, even when the zero cross ofthe induced voltage is not detected during the de-energized period, theperiod can be shifted to the energized period that is the same as thatof the immediately previous driving cycle, and therefore the rotor canbe securely rotated.

Third Embodiment Configuration of Entire Driving Circuit and EdgeDetecting Circuit of Single-Phase Brushless Motor

As described above, the edge detecting circuit 50 according to first andsecond embodiments of the present invention masks the both-edge signalEGrf with the mask signal MS which is acquired by delaying the highimpedance signal HZ by the delay time period D1 of the delay circuit 53,and outputs the edge detection signal EG. Thus, the zero-cross detectingcircuit starts the zero-cross detection after the delay time period D1(predetermined time period) has elapsed from the start of thede-energized period, thereby masking the zero cross occurs due to theregenerative current that flows when the period is shifted from theenergized period to the de-energized period.

However, in the edge detecting circuit 50, the mask signal MS falls witha delay of the delay time period D1 relative to the start of theenergized period. Thus, as depicted in FIG. 10, for example, immediatelyafter the zero cross of the induced voltage is detected, the zero crossis detected due to the influence of the driving current that has startedto be supplied to the driving coil 9, and the motor driving circuit 1 a(1 b) may malfunction due to such false detection.

As described above, the timing control circuit 16 switches between thepositive current and the negative current supplied by the output circuit20 to the driving coil 9, every time the odd-even bit LP[0] is changedin response to the edge detection signal EG.

However, when the zero cross occurs in the induced voltage before themask signal MS starts up after the delay time period D1 has elapsed fromthe start of the de-energized period, this zero cross is masked with themask signal MS. Further, during the energized period during which thedriving current is supplied to the driving coil 9, or while theregenerative current flows when the period is shifted from the energizedperiod to the de-energized period, in either case, the induced voltagegenerated across the driving coil 9 is unable to be detected accurately.Thus, as depicted in FIG. 11, for example, during the energized period,or when the zero cross occurs in the induced voltage before the masksignal MS rises during the de-energized period, the edge detectingcircuit 50 does not output the pulsed edge detection signal EG, and thusthe period cannot be shifted from the de-energized period to theenergized period by switching between the positive current and thenegative current.

Hereinafter, with reference to FIGS. 12 and 13, a description will begiven of configurations, capable of preventing malfunction even in theabove cases, of the entire driving circuit and the edge detectingcircuit of a single-phase brushless motor according to a thirdembodiment of the present invention.

A motor driving circuit 1 c depicted in FIG. 12 includes an edgedetecting circuit 70 in place of the edge detecting circuit 50 ascompared to the motor driving circuit 1 b according to a secondembodiment of the present invention. The odd-even bit LP [0] outputtedfrom the loop counter 14 is also inputted to the edge detecting circuit70.

The edge detecting circuit 70 depicted in FIG. 13 includes delaycircuits 71, 78, and 79, inverters (inverting circuits) 72 and 80, ANDcircuits 73, 81, and 83, an NOR circuit 74, a selecting circuit 75, adetermining circuit 76, an OR circuit (logical sum circuit) 77, and anRSFF (RS-flop flop) 82.

The comparison result signal CP is inputted to the delay circuit 71 andan output signal of the delay circuit 71 is inputted to the inverter 72.The comparison result signal CP and an output signal of the inverter 72are inputted to the AND circuit 73, and a rising edge signal EGr isoutputted from the AND circuit 73. Further, the comparison result signalCP and the output signal of the inverter 72 are also inputted to the NORcircuit 74, and a falling edge signal EGf is outputted from the NORcircuit 74.

The selecting circuit 75 is configured as a two-input, one-outputmultiplexer, and the odd-even bit LP[0] is inputted to a select controlinput thereof. The rising edge signal EGr is inputted to a data inputthereof corresponding to the case where the odd-even bit LP [0] is zero,and the falling edge signal EGf is inputted to its data inputcorresponding to the case where the odd-even bit LP[0] is one.

The mask signal MS outputted from the RSFF 82, together with thecomparison result signal CP and the odd-even bit LP [0], is inputted tothe determining circuit 76, and a pseudo edge signal EGp is outputtedfrom the determining circuit 76. An output signal of the selectingcircuit 75 and the pseudo edge signal EGp are inputted to the OR circuit77. An output signal of the OR circuit 77 and the mask signal MS areinputted to the AND circuit 83, and the edge detection signal EG isoutputted from the AND circuit 83.

The high impedance signal HZ is inputted to the delay circuit 78. Anoutput signal of the delay circuit 78 is inputted to the delay circuit79, and an output signal of the delay circuit 79 is inputted to theinverter 80. Further, output signals of the delay circuit 78 and theinverter 80 are inputted to the AND circuit 81. An output signal of theAND circuit 81 is inputted to an “S” input (set input) of the RSFF 82,and the edge detection signal EG is inputted to an “R” input (resetinput) thereof. The mask signal MS is outputted from the RSFF 82.

===Operation of Driving Circuit for Single-Phase Brushless Motor===

An operation will hereinafter be described of the driving circuit forthe single-phase brushless motor according to an embodiment of thepresent invention with reference to FIGS. 14 and 15 as appropriate. Theoperation of the motor driving circuit 1 c according to an embodiment ofthe present invention is similar to the operation of the motor drivingcircuit 1 b according to a second embodiment of the present inventionexcept for an operation of the edge detecting circuit 70.

The AND circuit 73 of the edge detecting circuit 70 detects the risingedge of the comparison result signal CP by acquiring a logical productof the comparison result signal CP and its delayed inverted signal(output signal of the inverter 72), and outputs the pulsed rising edgesignal EGr. Thus, the rising edge signal EGr indicates the timing of thezero cross at which the sign of the differential voltage V1−V2 changesfrom negative to positive.

Whereas, the NOR circuit 74 detects the falling edge of the comparisonresult signal CP by acquiring a negative logical sum of the comparisonresult signal CP and its delayed inverted signal, and outputs the pulsedfalling edge signal EGf. Thus, the falling edge signal EGf indicates thetiming of the zero cross at which the sign of the differential voltageV1−V2 changes from positive to negative.

The selecting circuit 75 outputs the falling edge signal EGf in eachodd-numbered driving cycle (LP [0]=1) in which the positive current issupplied to the driving coil 9. On the other hand, the selecting circuit75 outputs the rising edge signal EGr in each even-numbered drivingcycle (LP [0]=0) in which the negative current is supplied to thedriving coil 9.

The AND circuit 81 detects the rising edge of the output signal of thedelay circuit 78 by acquiring a logic product of the output signal ofthe delay circuit 78 and its delayed inverted signal (output signal ofthe inverter 80). Thus, the mask signal MS outputted from the RSFF 82goes high after the delay time period D1 of the delay circuit 78 haselapsed from the start of the de-energized period (the rising edge ofthe high impedance signal HZ). When the pulsed edge detection signal EGis outputted from the AND circuit 83, the period is shifted from thede-energized period to the energized period and the mask signal MS goeslow.

As such, in the motor driving circuit 1 c according to an embodiment ofthe present invention, the mask signal MS is low from the start of theenergized period to the time when the delay time period D1(predetermined time period) has elapsed from the start of thede-energized period. The zero-cross detecting circuit starts thezero-cross detection after the delay time period D1 has elapsed from thestart of the de-energized period, and when the zero cross is detected,the zero-cross detecting circuit ends the zero-cross detection. Thus, asdepicted in FIG. 14, for example, when the zero cross of the inducedvoltage is detected and the pulsed edge detection signal EG isoutputted, the mask signal MS goes low. Therefore, even when a zerocross occurs due to the driving current immediately thereafter, the zerocross is not detected. In the following, the time period during whichthe mask signal MS is low is referred to as “non-detection period”.

The determining circuit 76 determines whether the zero cross occurs inthe induced voltage during the non-detection period, based on the logiclevel of the comparison result signal CP at the start of the zero-crossdetection (the rising edge of the mask signal MS).

More specifically, during an odd-numbered driving cycle (LP [0]=1)during which the zero cross from positive to negative is detected andthe falling edge signal EGf is to be outputted, when the comparisonresult signal CP is low at the start of the zero-cross detection, it isdetermined that the zero cross occurs in the induced voltage during thenon-detection period. On the other hand, during an even-numbered drivingcycle (LP [0]=0) during which the zero cross from negative to positiveis detected and the rising edge signal EGr is to be outputted, when thecomparison result signal CP is high at the start of the zero-crossdetection, it is determined that the zero cross occurs in the inducedvoltage during the non-detection period. When determining that the zerocross occurs in the induced voltage during the non-detection period, thedetermining circuit 76 outputs the pulsed pseudo edge signal EGp at thestart of the zero-cross detection.

As such, the motor driving circuit 1 c according to an embodiment of thepresent invention outputs the pseudo edge signal EGp indicative of thedetermination result that zero cross occurs in the induced voltageduring the non-detection period, in addition to the rising edge signalEGr and the falling edge signal EGf indicative of the timing of the zerocross. The zero-cross detecting circuit outputs the edge detectionsignal EG when detecting the zero cross of the induced voltage duringthe de-energized period, and in addition thereto, also outputs the edgedetection signal EG at the start of the zero-cross detection when thezero-cross detecting circuit determines that the zero cross occurs inthe induced voltage during the non-detection period. Therefore, asdepicted in FIG. 15, for example, the pulsed edge detection signal EG isoutputted also when the zero cross occurs in the induced voltage duringthe non-detection period, and thus the period can be shifted to theenergized period by switching between the positive current and thenegative current.

As described above, in the motor driving circuits 1 a to 1 c, while thepositive current and the negative current are being supplied to thedriving coil 9 in an alternate manner with the de-energized periodtherebetween, in the normal mode after the starting up of thesingle-phase brushless motor, the length of the subsequent energizedperiod is determined at each time based on the driving cycle includingthe energized period for energizing the driving coil 9 and thesubsequent de-energized period, thereby being able to drive thesingle-phase brushless motor without using any position detectingelement such as a Hall element. Thus, miniaturization of the motor isenabled: by reducing the height of the motor by further reducing thethickness of the chip of the motor driving IC; and/or by mounting the ICon the exterior of the motor. Even when the IC is mounted on theinterior of the motor, the variation in the position for the IC to bemounted does not effect on the precision in detecting the rotationposition of the rotor, and the cost of the motor may be reduced bysimplifying the manufacture process of the motor, as well as reductionin cost of the IC can be reduced by reducing the testing man-hoursbefore shipment.

In the motor driving circuits 1 b and 1 c, when the zero cross of theinduced voltage is not detected during the de-energized period, thelength of the immediately previous energized period is determined to bethe length of the subsequent energized period, thereby shifting to theenergized period that is the same as that in the immediately previousdriving cycle, so that the rotor can be securely rotated.

In the starting-up mode from the starting up of the motor drivingcircuit to the time when the number of energizations of the driving coil9 reaches the predetermined number of times, the energized time periodis set in advance so as to be reduced with an increase in the number ofenergizations, thereby being able to smoothly start up the single-phasebrushless motor from its halting state to its high-speed rotation state.

Further, in the motor driving circuit 1 c, the detection of the zerocross is started after the delay time period D1 (predetermined timeperiod) has elapsed from the start of the de-energized period, and whenthe zero cross is detected, the detection of the zero cross is ended,thereby being able to mask such zero crosses as the zero cross caused bythe regenerated current flowing when the period is shifted from theenergized period to the de-energized period and the zero cross caused bythe driving current occurring immediately after the zero cross of theinduced voltage is detected.

Further, in the motor driving circuit 1 c, in the case where it isdetermined that the zero cross occurs in the induced voltage during thenon-detection period in addition to the case where the zero cross of theinduced voltage is detected during the de-energized period, the pulsededge detection signal EG is also outputted, thereby being able to switchbetween the positive current and the negative current, so that theperiod can be shifted to the energized period.

In the motor driving circuits 1 b and 1 c, when the main count value CNTreaches the full count value Tmax (first predetermined value), only themain counter 11 b is reset using the restart signal RES, and the periodis shifted to the energized period without switching between thepositive current and the negative current, thereby being able tosecurely rotate the rotor even in the case where the zero cross of theinduced voltage can not be detected during the de-energized period.

In the starting-up mode which is a period until the time when the loopcount value LP reaches the second predetermined value, the start-upcount values T1 to T10 are set in advance such that the energizationwidth is reduced with an increase in the loop count value LP, therebybeing able to control the energized period and the de-energized periodin the starting-up mode based on the main count value CNT and the loopcount value LP.

Furthermore, in the motor driving circuit 1 c, such a mask signal MS isgenerated that is low from the time when the energized period is startedto the time when the delay time period D1 has elapsed from the start ofthe de-energized period, thereby being able to mask, using the masksignal MS, such zero crosses as the zero cross caused by the regeneratedcurrent flowing when the period is shifted from the energized period tothe de-energized period and the zero cross caused by the driving currentflowing immediately after the zero cross of the induced voltage isdetected.

Further, the motor driving circuit 1 c generates the pseudo edge signalEGp indicative of the determination result that the zero cross occurs inthe induced voltage during the non-detection period based on the logiclevel of the comparison result signal CP at the start of the zero-crossdetection, thereby being able to output the pulsed edge detection signalEG even when the zero cross occurs in the induced voltage during thenon-detection period, and switch between the positive current and thenegative current and the period is shifted to the energized period.

In embodiments described above, the operation mode in a period when theloop count values LP is one to ten is given as the starting-up mode.However, the number “m” of loop count values LP to set the starting-upmode may be varied as appropriate. In this case, the number m ofstart-up count values T1 to Tm are set in advance respectively for theloop count values LP one to m, and are stored in the energized timeperiod setting register 13.

In second and third embodiments of the present invention, when the maincounter 11 b is reset in response to the restart signal RES, the periodis shifted to the energized period without switching between thepositive current and the negative current at every time, but it is notlimited thereto.

For example, a configuration may be such that a third counter circuit isfurther included that counts the number of instances where the restartsignal RES is outputted from the main counter 11 b, and such that whenthe count value reaches the third predetermined value, the main counter11 b is not reset thereafter. With such a configuration, in the casewhere such a state continues that the zero cross of the induced voltageis not detected during the de-energized period, the period is notshifted to the energized period. Thus, in the case where the rotor cannot be rotated due to the excessively great load on the motor, nocountermeasure taken for the motor against the dead point, or the like,the supply of the driving current to the driving coil can be stopped.

The above embodiments of the present invention are simply forfacilitating the understanding of the present invention and are not inany way to be construed as limiting the present invention. The presentinvention may variously be changed or altered without departing from itsspirit and encompass equivalents thereof.

What is claimed is:
 1. A driving circuit for a single-phase brushlessmotor, comprising: a driving signal generating circuit configured togenerate a driving signal for supplying, to a driving coil of thesingle-phase brushless motor, a first driving current and a seconddriving current opposite in direction to the first driving current, inan alternate manner with a de-energized period therebetween during whichneither of the first driving current or the second driving current issupplied to the driving coil; an output circuit configured to supply thefirst or the second driving current to the driving coil in response tothe driving signal; and a zero-cross detecting circuit configured todetect a zero cross of an induced voltage, generated across the drivingcoil, during the de-energized period, wherein while measuring a drivingcycle from a start of an energized period, during which the outputcircuit supplies the first or the second driving current to the drivingcoil, to a time when the zero-cross detecting circuit detects the zerocross, the driving signal generating circuit determines a length of asubsequent energized period based on the measured driving cycle, whenthe zero-cross detecting circuit detects the zero cross, and the drivingsignal generating circuit determines a length of an immediately previousenergized period as a length of a subsequent energized period, when thezero-cross detecting circuit does not detect the zero cross.
 2. Thedriving circuit for a single-phase brushless motor of claim 1, whereinthe driving signal generating circuit is configured to generate thedriving signal for supplying the first or the second driving currentfrom the output circuit to the driving coil only during an energizedtime period, until the number of energizations of the driving coil afterstarting-up reaches a predetermined number of times, the energized timeperiod set in advance so as to be reduced with an increase in the numberof energizations.
 3. The driving circuit for a single-phase brushlessmotor of claim 1, wherein the zero-cross detecting circuit is configuredto start detection of the zero cross after the predetermined time periodhas elapsed from a start of the de-energized period, and end thedetection of the zero cross when the zero cross is detected.
 4. Thedriving circuit for a single-phase brushless motor of claim 2, whereinthe zero-cross detecting circuit is configured to start detection of thezero cross after the predetermined time period has elapsed from a startof the de-energized period, and end the detection of the zero cross whenthe zero cross is detected.
 5. The driving circuit for a single-phasebrushless motor of claim 3, wherein the zero-cross detecting circuit isconfigured to determine whether or not the zero cross occurs in theinduced voltage during a non-detection period from the start of theenergized period to the start of the detection of the zero cross, andwherein when the zero-cross detecting circuit detects the zero cross andwhen the zero-cross detecting circuit has determined that the zero crossoccurs in the induced voltage during the non-detection period, thedriving signal generating circuit is configured to switch between thefirst driving current and the second driving current and cause the firstor the second driving current to start to be supplied from the outputcircuit to the driving coil.
 6. The driving circuit for a single-phasebrushless motor of claim 4, wherein the zero-cross detecting circuit isconfigured to determine whether or not the zero cross occurs in theinduced voltage during a non-detection period from the start of theenergized period to the start of the detection of the zero cross, andwherein when the zero-cross detecting circuit detects the zero cross andwhen the zero-cross detecting circuit has determined that the zero crossoccurs in the induced voltage during the non-detection period, thedriving signal generating circuit is configured to switch between thefirst driving current and the second driving current and cause the firstor the second driving current to start to be supplied from the outputcircuit to the driving coil.
 7. The driving circuit for a single-phasebrushless motor of claim 1, wherein the driving signal generatingcircuit includes a first counter circuit configured to count using apredetermined clock, and reset every time the zero-cross detectingcircuit detects the zero cross or when a count value reaches a firstpredetermined value, a register configured to store, as the drivingcycle, a count value acquired immediately before the first countercircuit is reset, every time the zero-cross detecting circuit detectsthe zero cross, and a timing control circuit configured to control theenergized period and the de-energized period by outputting the drivingsignal based on a count value of the first counter circuit, wherein thetiming control circuit is further configured to, every time thezero-cross detecting circuit detects the zero cross, switch between thefirst driving current and the second driving current, and cause thefirst or the second driving current to start to be supplied from theoutput circuit to the driving coil, when the count value of the firstcounter circuit reaches a value acquired by multiplying the drivingcycle stored in the register by a predetermined coefficient greater thanzero and smaller than one, cause both the first and the second drivingcurrents to stop being supplied from the output circuit to the drivingcoil, and when the count value of the first counter circuit reaches thefirst predetermined value, cause the first or the second driving currentto start to be supplied from the output circuit to the driving coilwithout switching between the first driving current and the seconddriving current.
 8. The driving circuit for a single-phase brushlessmotor of claim 7, wherein the driving signal generating circuit furtherincludes a second counter circuit configured to count the number ofenergizations of the driving coil from starting up, and wherein thetiming control circuit is further configured to, when the count value ofthe first counter circuit reaches a value set in advance so as to bereduced with an increase in a count value of the second counter circuit,cause both the first and the second driving currents to stop beingsupplied from the output circuit to the driving coil, during a timeperiod until a time when the count value of the second counter circuitreaches a second predetermined value.
 9. The driving circuit for asingle-phase brushless motor of claim 7, wherein the zero-crossdetecting circuit includes a differential amplifier circuit configuredto differentially amplify a voltage across the driving coil; acomparator configured to compare an output voltage of the differentialamplifier circuit and a predetermined reference voltage, and an edgedetecting circuit configured to detect a rising edge or a falling edgeof an output signal of the comparator, and output an edge detectionsignal, wherein the edge detecting circuit is further configured togenerate a mask signal for performing masking during a time period fromthe start of the energized period to a time when the predetermined timeperiod has elapsed from a start of the de-energized period, and mask theedge detection signal with the mask signal, to be outputted therefrom,and wherein the timing control circuit is further configured to, everytime the edge detection signal is outputted from the edge detectingcircuit, switch between the first driving current and the second drivingcurrent, and cause the first or the second driving current to start tobe supplied from the output circuit to the driving coil.
 10. The drivingcircuit for a single-phase brushless motor of claim 7, wherein thezero-cross detecting circuit includes a differential amplifier circuitconfigured to differentially amplify a voltage across the driving coil;a comparator configured to compare an output voltage of the differentialamplifier circuit and a predetermined reference voltage, and an edgedetecting circuit configured to detect a rising edge or a falling edgeof an output signal of the comparator, and output an edge detectionsignal, wherein the edge detecting circuit is further configured togenerate a mask signal for performing masking during a time period fromthe start of the energized period to a time when the predetermined timeperiod has elapsed from a start of the de-energized period, and mask theedge detection signal with the mask signal, to be outputted therefrom,and wherein the timing control circuit is further configured to, everytime the edge detection signal is outputted from the edge detectingcircuit, switch between the first driving current and the second drivingcurrent, and cause the first or the second driving current to start tobe supplied from the output circuit to the driving coil.
 11. The drivingcircuit for a single-phase brushless motor of claim 9, wherein the edgedetecting circuit is configured to determine whether or not the zerocross occurs in the induced voltage during a non-detection period,during which the edge detection signal is masked with the mask signal,based on an output signal of the comparator, and when determining thatthe zero cross occurs in the induced voltage during the non-detectionperiod, output the edge detection signal after the predetermined timeperiod has elapsed from the start of the de-energized period.
 12. Thedriving circuit for a single-phase brushless motor of claim 10, whereinthe edge detecting circuit is configured to determine whether or not thezero cross occurs in the induced voltage during a non-detection period,during which the edge detection signal is masked with the mask signal,based on an output signal of the comparator, and when determining thatthe zero cross occurs in the induced voltage during the non-detectionperiod, output the edge detection signal after the predetermined timeperiod has elapsed from the start of the de-energized period.